Detector apparatus of the two-terminal type supplied with rectified A.C. power the voltage of which can vary in a wide range, with load control by switching thyristors

ABSTRACT

A detector apparatus of the two-terminal type supplied with rectified A.C. power (e 1 , e 2 , v 1  v 2 , D 7  -D 10 ) the voltage of which can vary in a wide range, for controlling a series-connected load (CH), including at least one thyristor (TH 1 ) and a Zener diode (Z 3 ), a detector-control circuit assembly (CAP) associated with the load, the output (s) of which biases the base of a first transistor (T 1 ), a capacitor (C 5 ) serving as a power supply for the detector control circuit (CAP), and means for protection against overloads, which include a MOS-type transistor (T 3 ), a second transistor (T 2 ) connected to the grid of said MOS transistor, and a differential amplifier (A) connected in series with the base of said first transistor (T 1 ).

BACKGROUND OF THE INVENTION

The invention relates to detector apparatus of the two-terminal typesupplied with rectified AC power and including a sensor associated witha control circuit, which apparatus are series-connected with the load tobe controlled, and more particularly it relates to apparatus the supplyvoltage of which can vary in a wide range, e.g. from about 20 V to about240 V, and to supply means, means for controlling the output current,and means for protecting against overloads or shorts, which areincorporated in such apparatus.

As an example, the apparatus may be a proximity or presence detectorhaving a photocell, of the capacitive or other type.

In such apparatus, the load control is frequently carried out by gatingat least one thyristor whenever the diode provides a control signal,which causes a current, so called output current, having an intensitysufficient to control the load, to flow through the load in the circuit.

These apparatus generally include, in addition to the sensor and thecontrol circuit, means for rectifying the A.C current feeding theapparatus, resistors which are series-connected with the sensor-controlcircuit assembly and through with the latter is fed whenever the load isin its off-state, and at least one Zener diode connected across saidassembly and in series with the thyristor so as to define a referencevoltage.

In such a type of apparatus, it is important not to disturb the loadoperation by reducing the voltage across the apparatus whenever the loadis being controlled. The voltage across the apparatus, then so-called"waste voltage", must be as low as possible. Furthermore, since anapparatus of this kind must operate under quite variable supplyvoltages, e.g. from about 20 V to about 240 V, it is necessary tocontrol the current flowing through the circuit whenever the load is offso that its value remains negligible and substantially constantwhichever is the above-defined supply voltage; this current is thenreferred to as "residual current".

THE PRIOR ART

One of the drawbacks of prior art apparatus is that, whenever thethyristor is fired, its control can only be taken over when the currentflowing therethrough is near zero. This does not allow the circuit to beprotected whenever either an overload or short occurs while a loadcontrol order is provided by the sensor and thence the thyristor isconducting current.

OBJECT OF THE INVENTION

The object of the invention is to overcome this drawback by providing adetector apparatus of the two-terminal type including means forgenerating a control signal from information provided by a sensor,supply means series-connected with a load to be controlled, providing arectified A.C current the voltage of which may vary in a wide range, andmeans for controlling the load, which are connected both to said supplymeans and to said control signal generating means, said load controllingmeans including at least one thyristor and a Zener diode which areseries-connected in reverse directions, a transistor having an inputelectrode, an output electrode and a control electrode, means forconnecting the thyristor gate to said transistor input electrode, meansfor connecting the thyristor input electrode to the cathode of saidZener diode, means for connecting the thyristor output electrode to theanode of said Zener diode, means for connecting the control electrode ofthe transistor to the output of the said means for generating a controlsignal, a capacitor, means for connecting said capacitor to the cathodeof said Zener diode, and means for connecting said capacitor to theanode of said Zener diode, whereby said capacitor serves as a powersupply for said control signal generating means whenever the rectifiedcurrent flowing through the apparatus takes its minimum value, said loadcontrolling means further comprising means for limiting the intensity ofthe current through the apparatus, including a high-gain solid statecomponent which is series-connected with said thyristor, and adifferential amplifier the output of which is connected to saidtransistor control electrode, whereby said differential amplifier andsolid state component are so connected that the transistor, which isnormally blocked whenever a control order is provided by said controlsignal generating means, becomes saturated upon any overload or shortand thence blocks the thyristor.

In order to provide a residual current which is as low as possible andsubstantially constant, while supplying the apparatus with a voltagewhich can be selected within a wide range, the invention provides asecond transistor which is series-connected with said control input ofsaid solid state compoment and the base of which is, on one handconnected to the output of said differential amplifier, and, on theother hand, biased through a bridge consisting of a Zener diode and aresistor.

In order to achieve a waste voltage which is as low as possible, theinvention also provides a second thyristor connected in series with saidsolid state component and in parallel with the first-mentioned thyristorand said Zener diode which are series-and opposition-connected.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The various features and the advantages of the invention will becomeevident from the following disclosure taken in combination with theaccompanying single drawing which shows a diagram of an apparatus of thetwo-terminal type in accordance with a preferred embodiment of theinvention.

The circuit as shown in the appended drawing is supplied with AC voltagethrough a pair of supply terminals e₁ and e₂ connected to a full-waverectifier bridge, consisting of diodes D₇ -D₁₀, through a pair of supplylines v₁ and v₂, respectively, with one of which (v₁) isseries-connected a load CH, e.g. a relay. The rectifier bridge D₇ -D₁₀provides at its output a rectified voltage which feeds the remainder ofthe circuit through a pair of supply lines v_(DD) (positive pole) andV_(SS) (negative pole).

A CAP assembly consisting of a diode and a load control circuit andincluding, e.g. a phototransistor, has a pair of supply terminals,namely a positive terminal b₁ and a negative terminal b₂, and an outputs. This assembly is fed by said diode bridge through a transistor T₃,which may advantageously be of the MOS-type and the drain of which isdirectly connected to line V_(DD) and the source of which is connectedto positive terminal b₁ of the CAP assembly through a diode D₅, aresistor R₁₁ and a resistor R₈, while terminal b₂ is directly connectedto V_(SS). Transistor T₃ is biased through a resistor R₁₃ connectedbetween T₃ emitter and V_(DD).

The other end of T₃ emitter is connected to V_(SS) through a transistorT₂, e.g. of the NPN-type, via its collector-emitter junction, itscollector being connected to V_(SS).

T₃ source is connected to V_(SS) via D₅ through an opposition-connectedZener diode Z₂ and a resistor R₉ series-connected with Z₂, T₂ base beingconnected to the circuit path connecting Z₂ anode to R₉. T₃ source isalso connected to V_(SS) through a first thyristor TH₁ the cathode ofwhich is connected to a light-emitting diode DEL serving to signal theon- or off-state of CH, at the anode thereof, DEL cathode beingconnected to a Zener diode Z₃ having a Zener voltage lower than Z₂ andwhich is in opposition and connected to V_(SS) through threeseries-connected resistors R₁₄, R₁₅ and R₁₆, R₁₄ being connected to Z₃anode and R₁₆ being connected to V_(SS).

A second thyristor TH₂ which is connected in parallel with TH₁, DEL, Z₃and resistors R₁₄ and R₁₅ is provided for connecting T₃ source to V_(SS)through R₁₆. TH₂ gate is connected to Z₃ anode.

A Zener diode Z₁ is connected in parallel with terminals b₁ and b₂, itscathode being connected to b₁ , and thus limits the voltage which can beapplied to CAP assembly.

Output s biases, through a resistor bridge R₅, R₇ wherein R₅ isconnected to s and R₇ is connected to V_(SS), the base of a transistorT₁, e.g. of the NPN-type, the emitter of which is directly connected toV_(SS) and the collector of which is connected to V_(DD) through, inthis order, V_(DD), T₃, D₅, a resistor R₁₂ and a diode D₄ the cathode ofwhich is connected to T₁ collector. D₄ anode is, on one hand, as hereinabove stated, connected to R₁₂ and, on the other hand, connected to TH₁.T₁ collector is connected to V_(SS) through a capacitor C₄.

A capacitor C₅ serving as a supply storage for CAP assembly is connectedboth to the connecting point of resistors R₁₄ and R₁₅, and to terminalb₁ of CAP assembly through R₈. A diode D₆ the anode of which isconnected to DEL cathode and the cathode of which is connected to thatC₁ terminal which is connected to R₈ allows C₁ to be charged. CapacitorC₅ is connected to T₃ grid through a diode D₂ connected in series with aresistor R₁₀. Resistor R₁₀ is connected to T₃ grid and D₂ anode isconnected to that C₁ terminal which is connected to R₈.

The circuit also includes an operational amplifier A having a positivesupply terminal connected to V_(DD) through R₁₁, D₅ and T₃, and anegative supply terminal directly connected to V_(SS). Operationalamplifier A also has a pair of inputs "+" and "-", respectively, and anoutput S_(A).

The "-" input of A is connected to a resistor bridge R₂, R₁, connectedin parallel across terminals b₁, b₂ of CAP assembly, whereby resistor R₂is connected to b₁ and resistor R₁ is connected to b₂, thence to V_(SS).The "+" input of A is connected both to V_(SS) through a resistor R₃ andto output S_(A) of A through a resistor R₄. Output S_(A) is in turnconnected to T₁ base through a resistor R₆ and to T₂ base through acapacitor C₃. A diode D₃ provides connection between a resistor R₁₆,which is not connected to V_(SS), and the "+" input of A, D₃ cathodebeing connected to said "+" input and being also connected to V_(SS)through a capacitor C₂. A capacitor C₁ is connected in parallel with R₂and its charging is provided through a diode D₁ the anode of which isconnected to that C₁ terminal which is connected to the "-" input ofamplifier A and the cathode of which is connected to T₂ collector.

Finally, a non-linear resistor E is connected between A.C. power supplylines v₁ and v₂ downstream load CH.

Whenever the load (CH) is in its off-state, i.e. no load control orderis detected by the detector of CAP assembly, transistor T₃ is biased byR₁₃ and used as a current generator. Its source is maintained at aconstant potential set through a Zener diode D₂ the biasing current ofwhich is limited by a resistor R₉ series-connected with Z₂. The currentintensity through T₃ is controlled through auxiliary or secondtransistor T₂, which allows to maintain at low, minimum valve thecurrent through the load where there is a voltage of varying amplitudeat terminals e₁ and e₂, thus preventing this current from disturbing CHoperation. A portion of the current generated by T₃ serves to feed theCAP assembly the voltage accross which is maintained constant by meansof Zener diode Z₁. The remaining portion of the current generated by T₃flows through T₁, which is maintained in its saturated state since thebias provided at the output thereof has adjusted itself to such effect.

Whenever the detector of the CAP assembly receives a load control order,the order is transmitted to output s of the CAP assembly, which blocksT₁. The current provided by T₃ then charges capacitor C₄ through R₁₂ andD₄ until TH₁ gate reaches the potential necessary to fire TH₁. TH₁ thengoes into its conducting state and in turn charges C₅ until thepotential difference across C₅ becomes equal to Z₃ Zener voltage, whichis lower than that of Z₂. Once C₅ is charged, Zener diode Z₃ becomesconducting and the current flowing through Z₃ generates across resistorsR₁₄ and R₁₅ a potential difference sufficient to bias TH₂ gate so as torender TH₂ conducting. TH₂ then short-circuits TH₁, DEL and Z₃, as wellas resistors R₁₄ and R₁₅, thus reducing the waste voltage of the circuitupon occurence of a voltage drop through the diode bridge, increasedwith voltage drops through T₃, TH₂ and R₁₆. Resistances of R₁₄ and R₁₅are so selected that the potential increase across R₁₅ resulting from C₅charging current is not sufficient, under normal operating conditions,to bias TH₂ gate and fire TH₂, whereas the potential increase across R₁₄and R₁₅ in series, whenever Z₃ passes current, is sufficient to fireTH₂. This explains that TH₂ will become fired only when Z₃ is conductingcurrent.

Whenever TH₂ is conducting current, T₃ source is substantially broughtdown to the circuit low potential and T₃ grid biasing is then providedby capacitor C₅ which feeds the grid through D₂ and R₁₀. T₃ saturationis thus provided in spite of the low waste voltage. Capacitor C₅ alsoserves as a power supply storage for CAP assembly whenever TH₂ isconducting current since the voltage across the bridge is not sufficientat this time. Through R₁₆ flows a current substantially equal to thewhole current flowing through T₃ since the current derived by R₈ and CAPassembly is negligible. The voltage across R₁₆ thus indicates at alltimes the intensity of the current through the load. The potentialdifference across R₁₆ is applied through D₃ to the "+" input ofoperational amplifier A.

In normal operation, i.e. in the absence of any overload, this potentialis lower than the one applied to the "-" terminal through resistorbridge R₁, R₂ and output S_(A) is substantially at the circuit lowpotential.

Whenever an overload condition occurs, the current through T₃ increases,resulting in a corresponding increase of the potential difference acrossR₁₆, and thence of the potential of the "+" input. The latter potentialthen becomes greater than that of the "-" input, which causes A toswitch over. A voltage equal to the supply voltage of the differentialamplifier then appears at S_(A). Such a change in S_(A) potential causesC₃ to be charged through R₉. The charging current generates across R₉ asufficient potential difference to bias T₂ base, so that T₂ becomessaturated, as a result of which T₃ source is brought to a potentialsubstantially equal to the circuit low potential, and thus T₃ becomesblocked. T₂ is kept saturated as long as the C₃ charging currentgenerates a sufficient potential difference across R₉. T₃ blockinginduces TH₁ and TH₂ blocking since no current flows therethrough.

While at this time the potential difference across R₁₆ is zero, A outputis maintained at the same level as the circuit supply voltage becausethe "+" input potential is maintained greater than the "-" inputpotential through resistor bridge R₃, R₄ since resistances of R₁, R₂, R₃and R₄ have been selected to such effect. Also, capacitor C₁ becomescharged upon switching of its output S_(A) through T₂ whenever thelatter is saturated. Thus, C₁ helps to maintain A locking whenever suchlocking is provided by resistor bridge R₃, R₄ upon blocking of TH₁ andTH₂.

The occurence of a voltage at S_(A) results in T₁ switching to itssaturated state since its base is connected to S_(A) through resistorR₆. The circuit then operates as hereinabove described when no controlorder is provided. The current through the load becomes eventuallylimited to the current flowing through T₁ and the CAP assembly.

In order to put the circuit again into operation, the unlocking of Awill be achieved either by disconnecting one of the supply lines v₁ andv₂ of the apparatus, or by increasing the potential of A "-" input to apotential greater than its "+" input potential.

The above-described circuit thus effectively provides protection of theapparatus against overloads and shorts, when the load is beingcontrolled, by reducing the current flowing through the circuit to theresidual current level.

By using a MOS-type transistor, it is possible to provide a controlcircuit consuming only a negligible power with respect to the currentthrough the load, thus not disturbing operation of the latter. Indeed,the grid current necessary to control the MOS transistor is in the rangeof a hundred nanoamperes (from 100 to 200 nA), whereas the currentthrough the transistor channel can reach intensities in the range of oneampere. Another feature of MOS transistors is that they can bearvoltages up to several hundred volts. Such a feature allows use of atransistor of this kind in circuits the supply voltage of which can varyin a substantial range (e.g., about 20 V R.M.S. to about 240 V R.M.S.).In the device according to the invention, both features have been used.Indeed, the MOS-type transistor serves as a power source with a varyingvoltage, in normal operation, and helps to protect the circuit in caseof an overload or a short-circuit, while consuming only a very lowcurrent for control thereof. Thus, the proposed device consumes onlylittle power for the control portion of its operation, which is one ofthe desired goals in a circuit of this kind.

When the control order provided by the detector of the CAP assemblyfires thyristor TH₁ while there is a load short-circuit, diode DEL andcapacitor C₅ could be destroyed if protecting means of the overallcircuit were set to operate with current levels greater than thosepermissible for these two components. In order to prevent such adestruction, the resistance of R₁₅ is so selected that the potentialdifference across it be sufficiently high to cause TH₂ firing whenever acurrent the level of which is close the permissible limit of both C₅ andDEL flows through R₁₅, since TH₂ derives current as above described.

Non-linear resistor E provides protection of the apparatus againstoverloads of inductive origin which may occur across load CH uponblocking of transistor T₃ when CH includes inductances.

The above-described circuit thus effectively provides a two-terminalapparatus the waste voltage of which is low in normal operation, by useof a second thyristor, and which is protected against overloads andshorts by control of the current intensity through the thyristors, bymeans of the differential amplifier associated with the MOS-typetransistor. This circuit also has the advantage to protect those circuitcomponents for which the permissible current level is lower than thelevel for which the protection has been designed, in case of firingduring a load short-circuit, by putting the second thyristor intooperation, which results in a derivation therethrough of the currentwhich could have destroyed said components. Finally, by using T₃ as apower source, the apparatus can operate in a voltage range, e.g. from 20to 240 V A.C. since the current feeding the internal circuits of theapparatus, which is provided by T₃, is constant and independent fromsaid voltage.

It should be understood that the above-described circuit may be embodiedin various forms without departing from the scope of the invention; asan example, the MOS-type transistor can be replaced with a high-gainpower Darlington circuit; however, as the gain thereof is lower than thegain of the MOS-type transistor, the current level required to controlit will be higher.

I claim:
 1. A detector apparatus for controlling the flow of currentthrough a load in dependence with information provided by a sensor, saiddetector apparatus comprising:(i) signal generating means (CAP) forgenerating an output signal from the said information, said signalgenerating means having first (b₁) and second (b₂) power supply inputsand a signal output (s); (ii) first and second power supply terminals(e₁ e₂), the detector apparatus having first and second terminals, thefirst terminal of the apparatus being connected to the first powersupply terminal (e₁) through the load and the second terminal of theapparatus being connected to the second power supply terminal (e₂);(iii) rectifier means (D₇ -D₁₀) having a pair of input terminalsconnected accross the first and second terminals of the apparatus and apair of output terminals and first (V_(DD)) and second (V_(SS)) powersupply lines connecting the respective output terminals of the rectifiermeans to the respective power supply inputs (b₁ b₂) of the signalgenerating means; (iv) a high gain solid state component (T₃) having asource (S), a drain (D) and a gate (G), said drain being connected tothe first power supply line (V_(DD)) and said gate being connected tothe first power supply (V_(DD)) of the rectifier means through a biasingresistor (R₁₃); (v) circuit means, including a first thyristor (TH₁)having a gate and a Zener diode (Z₃) connected in series and inopposition, said circuit means connecting the source (S) of the saidhigh gain solid state component (T₃) to the second power supply line(V_(SS)), said Zener diode (Z₃) having an anode and a cathode; (vi) atransistor (T₁) having an input electrode, and output electrode which isconnected to the said second power supply line (V_(SS)) and a controlelectrode; and means (D₄) for connecting the gate of the said firstthyristor (TH₁) to the said input electrode; (vii) differentialamplifier means (A) having first and second inputs and an output, theoutput of the said differential amplifier means being connected to thecontrol electrode of the said transistor (T₁), a resistor bridge (R₁ R₂)connecting the power supply inputs (b₁ -b₂) of the signal generatingmeans to the first input of the differential amplifier means, and firstresistance means (R₃) connecting the second power supply line (V_(SS))to the second input of the differential amplifier means; (viii) a firstcapacitor (C₅); means (D₆) for connecting said capacitor to the cathodeof the Zener diode (Z₃), means (R₁₄) for connecting said first capacitorto the anode of the Zener diode (Z₃), and means (R₈) connecting thecapacitor to the first power supply input (b₁) of the signal generatingmeans; (ix) means (R₁₄ R₁₅ R₁₆ D₃), connecting the anode of the Zenerdiode (Z₃) to the second input of the differential amplifiermeans,whereby the said transistor (T₁) which is normally blockedwhenever the signal generating means provide an output signal, becomessaturated upon occurrence of an overload or short through the load, andconsequently, the said first thyristor (TH₁) is blocked.
 2. A detectorapparatus as claimed in claim 1, wherein second resistance means (R₄)connect the second input and the output of the said differentialamplifier means and the said means connecting the anode of the Zenerdiode (Z₃) to the second input of the differential amplifier meansinclude third resistance means (R₁₄ R₁₅ R₁₆) whereby the output of thesaid differential amplifier means switches from a first potential levelto a second potential level substantially higher than the firstpotential level upon occurrence of an overload or short through theload, the said second potential level being sufficient for causing thesaid transistor to become saturated.
 3. A detector apparatus as claimedin claim 2, wherein the said resistor bridge includes a first resistor(R₂) connecting the first power supply input (b₁) of the singalgenerating means and a second capacitor (C₁) is connected accross thesaid first resistor (R₂).
 4. A detector apparatus as claimed in claim 1,further including a second transistor (T₂) having an input electrode, anoutput electrode and a base, the output electrode of said secondtransistor being connected to the second power supply line (V_(SS)), theinput electrode of said second transistor being connected to the gate ofsaid high gain solid state component (T₃), and means (C₃) connecting thebase of said second transistor to the output of said differentialamplifier means.
 5. A detector apparatus as claimed in claim 4, whereinbiasing bridge means, including a further Zener diode (Z₂) and aresistor (R₉) connected between the source of the said high gain solidstate component (T₃) to the second power supply line (V_(SS)), arelinked to the base of the said second transistor (T₂).
 6. A detectorapparatus as claimed in claim 1, said apparatus further comprising asecond thyristor (TH₂) having an anode, a cathode and a gate, the anodeof said second thyristor (TH₂) being connected to the source of saidhigh gain solid state component (T₃), the gate of said second thyristorbeing connected to the anode of the said Zener diode (Z₃) and thecathode of the said second thyristor (TH₂) being connected to the saidsecond power supply line (V_(SS)) through a resistor (R₁₆).
 7. Adetector apparatus as claimed in claim 6, wherein the anode of the saidZener diode is connected to the second power supply line (V_(SS))through first and second serially connected resistors (R₁₄ R₁₅), havinga junction point, the first capacitor (C₅) is connected to the saidjunction point, and the resistor (R₁₆) which connects the cathode of thesecond thyristor (TH₂) to the second power supply line (V_(SS)) isconnected to the said second resistor (R₁₅).
 8. A detector apparatus asclaimed in claim 1, wherein the said high gain solid state component(T₃) is a MOS transistor.